The present invention relates to an ion flow forming system.
More particularly, the present invention relates to a method and apparatus in, e.g., a plasma processing system, for attracting only positive ions from a plasma and repelling electrons and negative ions to the plasma, thereby forming a positive ion flow directed toward a target object.
Conventionally, as a plasma processing system, a plasma etching system, a plasma CVD system, a plasma ashing system, a plasma cleaning system, and the like are widely known. As such a plasma processing system (to be referred to as a plasma system hereinafter), a system, e.g., a diode parallel plate plasma enhanced system, in which a plasma generation chamber and a plasma processing chamber are integrally formed, and a system, e.g., an ECR plasma enhanced system, in which a plasma generation chamber and a plasma processing chamber are separated, are available.
In the plasma system in which the plasma genera- tion chamber and the plasma processing chamber are separated, a mechanism that guides a plasma generated in the plasma generation chamber or charged particles (e.g., ions) in the plasma to the plasma processing chamber is required. FIG. 6 shows an ECR plasma etching system. In the ECR plasma etching system, a processing chamber 100 is formed in a hermetic processing vessel 102 which can be opened and closed. A susceptor 104 is arranged in the processing vessel 102, and a target object W (e.g., a semiconductor wafer or an LCD glass substrate) is placed on the susceptor 104 through an attraction means, e.g., an electrostatic chuck 106. The electrostatic chuck 106 is formed by mounting a plate electrode 106a between thin films made of an insulating material, e.g., a polyimide resin. When a high-voltage power is applied to the plate electrode 106a from a DC power supply 106 b, the wafer W is attracted by the susceptor 104 with the Coulomb force.
The susceptor 104 is provided with a temperature adjusting means comprising a cooling unit 108, a heater 110, and the like in order to adjust the wafer W to a predetermined temperature. A heat transfer gas supply means 112 is arranged in the susceptor 104. A heat transfer gas (e.g., helium gas) is supplied to the wafer W from the lower surface through a plurality of holes in the electrostatic chuck 106, so that the heat transfer efficiency from the susceptor 104 to the wafer W is increased. An RF power supply 116 is connected to the susceptor 104 through a matching circuit 114 to apply a bias RF power to the susceptor 104.
An inlet pipe 118 for introducing a predetermined process gas (a gas mixture of, e.g., carbon fluoride gas, oxygen gas, and argon gas) into the processing chamber 100 is connected to the side wall of the upper portion of the processing vessel 102. An exhaust pipe 120 communicating with an evacuating means (not shown) is connected to the lower portion of the processing vessel 102.
A plasma generation chamber 122 for generating an ECR plasma is connected to the upper portion of the processing chamber 100. A microwave generation chamber 134 is connected to the plasma generation chamber 122 through a waveguide 130. An inlet pipe 124 for introducing a plasma generation gas (e.g., argon gas) B is connected to the upper wall of the plasma generation chamber 122. The gas in the processing chamber 100 and the plasma generation chamber 122 is exhausted by the evacuating means through the exhaust pipe 120. Predetermined process gases are introduced from the inlet pipe 118 and the inlet pipe 124 into the processing chamber 100 and the plasma generation chamber 122, respectively.
A cooling means 126 is arranged on the outer surface of the side wall of the plasma generation chamber 122, and heat generated in the plasma generation chamber 122 is radiated. A magnetic coil 128 is arranged outside the cooling means 126 to surround the plasma generation chamber 122.
The plasma generation chamber 122 is connected to the microwave generation chamber 134 through the waveguide 130 that propagates the microwave. A microwave (e.g., a 2.45-GHz microwave) oscillated by the magnetron (not shown) of the microwave generation chamber 134 propagates to the plasma generation chamber 122 through the waveguide 130 and an insulating wall 132. Electric discharge is excited in the plasma generation chamber 122 by the propagating microwave. A magnetic field of, e.g., 875 Gauss, is applied to the interior of the plasma generation chamber 122 by the magnetic coil 128. During electric discharge, the electrons perform cyclotron motion to generate the ECR plasma for the plasma generation gas B.
Since the predetermined process gas A is introduced into the processing chamber 100, the reactive gas in the process gas is dissociated due to the function of the plasma (electrons) generated in the plasma generation chamber 122, to generate radicals.
A bias RF power is applied from the RF power supply 116 to the susceptor 104 in the processing chamber 100 through the matching circuit 114, and the interior of the processing chamber 100 is evacuated through the exhaust pipe 120. Therefore, the plasma and radicals generated in the plasma generation chamber 122 are guided onto the susceptor 104. A target film (e.g., a silicon oxide film) on the wafer W placed on the susceptor 104 is etched by the plasma and radicals.
This ECR plasma processing system is more suitable to advanced micropatterning of a target object than the conventional diode parallel plate plasma enhanced system and the like. The ECR plasma processing system can easily control etching shape ranging from anisotropic etching to complete isotropic etching. Also, since the ionization rate is high, high-speed etching with less damage can be performed with a low ion energy. Furthermore, since no-electrode discharge is utilized in the processing chamber 100, contamina- tion is few.
In such a plasma processing system in which the plasma generation chamber and the plasma processing chamber are separated, the ions in the plasma generated in the plasma generation chamber must be efficiently attracted into the processing chamber in order to increase the plasma processing efficiency. In the system shown in FIG. 6, however, not only ions necessary for plasma processing but also electrons are diffused and attracted from the plasma generation chamber simultaneously, and are introduced to the processing target in the plasma processing chamber.
Since a force that maintains the electrical neutral state acts between the ions and electrons, it is very difficult to separate the ions and electrons and to introduce only the ions into the processing chamber efficiently. When the electrons and ions (charged particles) are mixed, it is not easy to control only the charged particles with a mechanism combined with an electrode. The advantage of separating only the ions from the plasma arises from this respect. In the plasma ion source, to separate and extract only the ions from the plasma is a prerequisite. In plasma CVD, high-energy injected ions also have an advantage of making the film dense. Inversely, however, if the ion energy is excessively high or the number of ions is excessively large, the ions largely damage the film, which is a disadvantage. In another point of view, ions also have an effect of increasing the film deposition rate (ion induced deposition). When the effect of ion etching is excessively large, an underlying different film is also etched to cause contamination. In any case, to control the injecting ion energy is significant. In the ion source, to control the injecting ion energy is indispensable, as a matter of course.
Furthermore, in the system shown in FIG. 6, it is difficult to control ions mixed with electrons to a desired state, i.e., to cause them to be injected in a desired direction. Therefore, various types of ion flow control means such as an electric field generating means for generating a predetermined electric field in the plasma processing chamber are required.
It is an object of the present invention to effectively attract ions from a plasma generated by a plasma generation mechanism and to direct the ions toward a wafer (substrate).
It is another object of the present invention, in a plasma processing system in which a plasma generation chamber and a plasma processing chamber are separated, to effectively attract ions from a plasma generated by a plasma generation mechanism and to direct the ions toward a target object.
It is still another object of the present invention to solve the above drawbacks in a conventional plasma processing system and its plasma processing method.
It is still another object of the present invention to selectively direct only the ions in the plasma generated in the plasma generation chamber into the plasma processing chamber, so that the target object is efficiently processed with the ions.
It is still another object of the present invention to provide a novel, improved ion flow forming method and introducing apparatus that can attract a relatively large number of ions with a relatively small power.
When a constant potential gradient is continuously applied to a portion from which the ions are to be attracted, the following problem can be explained. The ions that have reached onto the electrode through free motion start to receive an attraction force to a certain degree. Accordingly, the ions also receive a force in the opposite direction with which the ions are dragged by the electrons. For this reason, in this case, the ions cannot be easily attracted. According to the present invention, this problem is solved by repeating the following operations between the electrodes:
(1) ambipolar diffusion (thermal diffusion): without potential gradient
(2) charge separation (ion acceleration): with potential gradient
Only the ions are efficiently charge-separated from the plasma introduced to the space between the electrodes.
The ion flow formed by the present invention can be used in various types of applications. For example, an ion flow having a reduced diameter can be used for implantation, and an ion flow having an enlarged diameter can be used for film deposition (ECR CVD).
According to the first aspect of the present invention, there is provided an ion flow forming method of attracting ions from a plasma generated in a plasma generation chamber and forming a flow of the ions, comprising the steps of:
(a) generating the plasma in the plasma generation chamber having a plasma diffusion outlet port;
(b) moving the plasma, generated in the plasma generation chamber, outside the plasma generation chamber through the plasma diffusion outlet port by diffusion;
(c) applying, to the plasma which has moved outside the plasma generation chamber, an electric field in such a direction to repel electrons in the plasma toward the plasma diffusion outlet port and to attract the ions in the plasma in a direction opposite to the electrons, for a shorter period of time than in the steps (a) and (b); and
(d) directing the attracted ions toward a target object.
According to the second aspect of the present invention, there is provided an ion flow forming method according to the first aspect, wherein the steps (a) to (d) are repeatedly performed in this order.
According to the third aspect of the present invention, there is provided an ion flow forming method according to the first aspect, wherein at least one of the steps (a) to (d) is performed constantly.
According to the fourth aspect of the present invention, there is provided an ion flow forming method according to the first aspect, wherein the step (c) is performed by applying different voltages to two electrodes arranged at the plasma diffusion outlet port of the plasma generation chamber.
According to the fifth aspect of the present invention, there is provided an ion flow forming method according to the fourth aspect, wherein
the step (c) is performed by applying the different voltages to the two electrodes arranged at the plasma diffusion outlet port of the plasma generation chamber in a pulsed manner, and
the step (d) is performed by stopping, after the ions are attracted from a space between the two electrodes, application of the voltages to the two electrodes.
According to the sixth aspect of the present invention, there is provided an ion flow forming method according to one of the first to third aspects, further comprising the step (e), having a duration considerably shorter than the step (c), between the steps (b) and (c), wherein
the step (e) comprises applying a bias to a first electrode so as to generate an electric field in a direction opposite to that in the step (c) in order to control the ions as a target.
According to the seventh aspect of the present invention, there is provided an ion flow forming method according to any one of the first to third aspects, wherein the step (d) is performed by applying, to a third electrode arranged between the two electrodes and the target object, at least one of an ion accelerating voltage and an ion beam convergence voltage.
According to the eighth aspect of the present invention, there is provided an ion flow forming method according to the fourth aspect, wherein the step (d) comprises the step of dispersing an ion flow in a path of the ions to reach the target object from the two electrodes.
According to the ninth aspect of the present invention, there is provided an ion flow forming method according to the eighth aspect, wherein in the step (c), when the ions contain an ion having a mass different from a predetermined mass, a pulse ratio of an ion acceleration time to a plasma diffusion time is not altered but a period is altered by either one of frequency modulation and amplitude modulation, thereby attracting the ion having the different mass as well.
According to the 10th aspect of the present invention, there is provided an ion flow forming method according to any one of the first, fourth, and fifth aspects, wherein in the step (d), the target object to which the attracted ions are directed is a silicon wafer with a circuit pattern formed thereon.
According to the 11th aspect of the present invention, there is provided an ion flow forming method according to any one of the first, fourth, and fifth aspects, wherein the step (a) is the step of generating the plasma by electron cyclotron resonance.
According to the 12th aspect of the present invention, there is provided an ion flow forming method according to the 11th aspect, wherein the step (c) comprises blocking at least one of introduction of a microwave for generation of an ECR plasma and an external magnetic field.
According to the 13th aspect of the present invention, there is provided an ion flow forming apparatus for attracting ions from a plasma generated in a plasma generation chamber and forming a flow of the ions, the apparatus comprising:
the plasma generation chamber having a plasma diffusion outlet port;
a processing chamber arranged to oppose the plasma diffusion outlet port and accommodating a target object;
two electrodes arranged between the plasma diffusion outlet port of the plasma generation chamber and the target object in the processing chamber; and
a potential control unit for controlling potentials of the two electrodes, the potential control unit serving
in a diffusion step of moving the plasma, generated in the plasma generation chamber, outside the plasma generation chamber through the plasma diffusion outlet port by diffusion, to perform a control operation so as to make the potentials of the two electrodes equal,
in an ion attraction step of repelling electrons in the plasma, which has been diffused outside the plasma generation chamber and moved to a space between the two electrodes, toward the plasma generation chamber and attracting the ions
in the plasma toward the processing chamber, to apply, to the two electrodes, different voltages in a pulsed manner so as to form an electric field, which allows the ion attraction step to be performed, in a space between the two electrode; and
in the ion flow formation step of directing the attracted ions toward the target object accommodated in the processing chamber, to control potentials of the electrodes not to form an electric field which acts to repel the attracted ions into the plasma.
According to the 14th aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein generation of the plasma, diffusion of the plasma, attraction of the ions, and formation of the ion flow are sequentially repeated.
According to the 15th aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein at least one of generation of the plasma and formation of the ion flow is constantly performed.
According to the 16th aspect of the present invention, there is provided an ion flow forming apparatus according to any one of the 14th and 15th aspects, further comprising a short-duration step, having a duration considerably shorter than that of the diffusion step, between the diffusion step and the ion attraction step, wherein in the short-duration step, a bias is applied to a first electrode so as to generate an electric field in a direction opposite to that in the ion attraction step in order to control the ions as a target.
According to the 17th aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein the potential control unit controls potentials of the plasma generation chamber and the processing chamber in addition to potentials of the two electrodes.
According to the 18th aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein the processing chamber accommodating the target object comprises an electrode for dispersing the ion flow between the electrodes and the target object.
According to the 19th aspect of the present invention, there is provided an ion flow forming apparatus according to the 18th aspect, wherein the ion flow is used for processing other than ion plantation.
According to the 20th aspect of the present invention, there is provided an ion flow forming apparatus according to the 18th aspect, wherein the electrode for dispersing the ion flow is an electrode with a two-layer structure in which two types of needle-like electrodes to which different potentials are to be applied are arranged alternately.
According to the 21st aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein each of the electrodes has such a thickness that decreases gradually toward an aperture through which charged particles pass.
According to the 22nd aspect of the present invention, there is provided an ion flow forming apparatus according to the 13th aspect, wherein in the ion flow formation step, when the ions contain an ion having a mass different from a predetermined mass, a pulse ratio of an ion acceleration time to a plasma diffusion time is not altered but a period is altered by either one of frequency modulation and amplitude modulation, thereby attracting the ion having the different mass as well.
According to the 23rd aspect of the present invention, there is provided an ion flow forming apparatus according to one of the 11th, 14th, and 15th aspects, wherein the target object accommodated in the processing chamber is a silicon wafer.
According to the 24th aspect of the present invention, there is provided an ion flow forming apparatus according to one of the 11th, 14th, and 15th aspects, wherein the target object accommodated in the processing chamber is a silicon wafer with a circuit pattern formed thereon.
According to the 25th aspect of the present invention, there is provided an ion flow forming apparatus according to one of the 11th, 14th, and 15th aspects, wherein the plasma generation chamber comprises a mechanism for generating the plasma by electron cyclotron resonance.
According to the 26th aspect of the present invention, there is provided an ion flow forming apparatus according to one of the 11th, 14th, and 15th aspects, wherein
the plasma generation chamber comprises a mechanism for generating the plasma by electron cyclotron resonance, and
in ion attraction, at least one of introduction of a microwave for generation of an ECR plasma and application of an external magnetic field is blocked.